The invention relates to injection molded articles and more specifically to closure rings fabricated of fiberfilled plastic which exhibit a coefficient of expansion that, circumferentially, is substantially equal to that of glass.
The components utilized for home preservation of fruit and vegetables have undergone remarkably little change in decades. A metallic lid with a resilient elastomer gasket, a threaded retaining ring and a complementarily threaded glass container typically constitute these components. The popularity of this food preservation system is matched by its routinely high success rate. The food storage scheme is not without problems, however, and they typically relate to the retaining ring and its removal.
Typical prior art canning rings are fabricated of steel or other suitable metal and are subject to corrosion and rusting. This problem may be compounded in several ways. First of all, the metal ring may be exposed to especially corrosive vapors emitted from the container during processing. Numerous small corrosion sites may thus be formed when the ring is first used. Secondly, processed and sealed containers are typically stored in basements and other areas of relatively high humidity. Deterioration, once begun, is typically exacerbated under these storage conditions. Finally, the containers may be stored for extended periods of time, often for as long as several years. During this time, corrosion may render the metal ring and regions of the glass container and lid in contact with it aesthetically unappealing.
Deterioration of the metal is not solely a cosmetic problem, however. Such corrosion may render removal of the ring difficult or even dangerous inasmuch as extended storage may tightly fix the ring to the glass container. The user may then resort to hand tools and other mechanical devices which are not suited for such tasks in an attempt to remove the ring.
One solution to this problem has been the removal of the metal canning ring subsequent to processing and cooling. This solution obviously alleviates corrosion and removal problems but results in increased vulnerability of the sealed containers to accidental loss of seal and subsequent content spoilage.
Another approach has been the utilization of canning rings fabricated of various plastics. Plastic rings enjoy exceptional freedom from rusting, corrosion and attack by various foods. Such rings, however, exhibit mechanical characteristics which seriously limit their use. Generally, suitable polymeric resins have a substantially higher thermal coefficient of expansion than does the glass from which conventional canning containers are fabricated. The rings, therefore, expand at a greater rate than the container finish to which they are threadably secured. Given the approximately 170.degree. F. temperature difference from ambient temperature to processing temperature to which the rings and containers are subjected, the disparity between the thermal expansion rates of the plastic and glass cause the canning ring to loosen and even dislodge from the container finish. In the first instance, the previously properly applied torque is lost and in the latter, the container contents are either partially harmed or completely destroyed.